This year, Medicare’s open enrollment overlaps with open enrollment for the new insurance marketplaces or exchanges created under the Affordable Care Act, also commonly referred to as Obamacare — but don’t let that throw you. Medicare’s 50 million-plus beneficiaries, most of them seniors, will steer clear of the marketplaces.

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Q: I have Medicare. Can I use my online state insurance marketplace to compare and buy a Medicare Advantage, supplement or prescription plan?

A: No, the marketplaces (also known as health exchanges) are not for Medicare beneficiaries. They are mostly for uninsured Americans and do not offer Medicare Advantage, medigap supplemental policies or Part D prescription plans. Medicare is not changing because of the marketplaces. For a medigap or Medicare Advantage plan, consult www.medicare.gov.

Q: What if I mistakenly sign up for insurance on the marketplace, will my Medicare coverage be automatically canceled?

A: No, if you have Medicare coverage, you won’t qualify for insurance on the marketplace. But if you do sign up for a plan accidentally, cancel the marketplace policy.

Q: But I’m a Medicare beneficiary, and someone contacted me and said I could buy insurance through the marketplace. What’s up?

A: It’s illegal for someone to knowingly sell a Medicare beneficiary a marketplace plan. Watch out for scammers during open enrollment. Do not share your Medicare number or personal information with anyone who says he or she can sell you a plan through the marketplace.

Q: Can I get the premium tax credit that people get when they buy insurance on the marketplaces?

A: If you’re enrolled in Medicare, you’re not eligible for the tax credits that some people qualify for on the marketplaces, but you already get a substantial break on costs. The overall costs of care under Medicare Part B, which pays doctors’ visits, and Part D, the prescription drug benefit, are subsidized 75 percent from federal general revenues. Plus, if you’re a Medicare beneficiary with limited resources and income, you may qualify for low-cost Part D drug coverage under the Extra Help program. Go to www.ssa.gov, call 800-772-1213 or visit your local Social Security office.

Q: I’ve just become eligible for Medicare, but I haven’t signed up yet and haven’t started collecting Social Security. Can I choose coverage on the marketplace instead of Medicare?

A: Yes, but be aware that if you fail to sign up for Medicare during your initial seven-month enrollment period — the three months before the month you turn 65, your birthday month and three months after your 65th birthday — you may have to pay a late enrollment penalty for as long as you have Medicare. Also, if you don’t enroll in Medicare Part B during your initial enrollment period, you can sign up only during what’s called the general enrollment period — Jan. 1 through March 31 — and your coverage won’t begin until July of that year.

Q: I’ll turn 65 next year and will become eligible for Medicare, but I don’t have health insurance now. Can I use the marketplace?

A: Yes, you’re uninsured and can buy a plan on the marketplace now that will be effective Jan. 1. Once you receive Medicare coverage, you should cancel the marketplace plan.

Q: I’m 65, a legal immigrant with a green card and have lived in this country for three years. Can I get Medicare coverage?

A: No, Medicare requires that you have lived in the United States continuously for five years. You may qualify for a health insurance plan on the marketplace, which does not have a residency waiting period.

Q: I’m 65 and Medicare-eligible, but I’m still working and covered by my employer’s health plan. My employer says she may terminate the company plan next year. What are my options?

A: If you didn’t sign up for Medicare Part A or Part B when you were first eligible because you were covered by a group plan based on current employment — yours or a spouse’s — you can sign up for Part A or Part B (or both) anytime you’re still covered by the group plan or during an eight-month period that begins the month after your coverage ends.

Q: I’m eligible for Medicare but didn’t sign up on time, and I haven’t bought insurance through the marketplace. Will I have to pay a fine?

A: Yes, if you’re uninsured and don’t qualify for an exemption to the requirement that everyone carry health insurance in 2014, you will have to pay a penalty. Exemptions include being a member of a federally recognized Indian tribe or having income too low to file a tax return.

Q: I have only Medicare Part A. Do I need to buy more insurance to meet the legal requirement that I have insurance?

A: No, whether you’re in a traditional Medicare or a Medicare Advantage plan, you meet the insurance requirement.

Q: I’m 60 and retired, but I’m too young for Medicare. I get my insurance through my former employer’s retiree health plan. Do I need to get additional coverage on the marketplace to comply with the health law?

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Q: I’m not thrilled with my plan, but there are a lot of choices. Where do I start?

A: Use the Plan Finder tool at www.medicare.gov to compare costs and benefits for each plan available in your area. Details of 2014 plans are available now. If you need personal help, call your State Health Insurance Assistance Program (SHIP). Contact information is at www.shiptalk.org. If you have Medicare Advantage or a Part D prescription drug plan, you should have received a notice of changes for 2014 in the mail. It will tell you whether your premiums, deductibles, copays and benefits will change next year.

Q: Can’t people change their Medicare coverage later than December?

A. Yes, between Jan. 1 and Feb. 14 every year, people with Medicare Advantage plans can leave their plans and switch to traditional Medicare, if they choose. In specific circumstances, such as a move, people can change Medicare coverage anytime.

Q: I’m happy with my current Medicare choices. What do I do during open enrollment?

A: Not a thing. Your current choices will continue next year.

Q: Where can I find more Medicare information?

A: For enrollment information, go to Social Security’s website, www.ssa.gov or call 800-772-1213. For coverage information, go to www.medicare.gov or call 800-MEDICARE (800-633-4227).

Marsha Mercer is a freelance writer in the Washington, D.C., area who covers health policy.